Method of growing carbon nanotube and carbon nanotube growing system

ABSTRACT

When growing carbon nanotubes, a substrate is delivered into a thermal CVD chamber whose internal temperature is a room temperature, and a mixed gas of an inert gas and a raw gas is introduced in the inside thereof. After a pressure inside of the chamber is stabilized at 1 kPa, the temperature in the chamber is raised to 510° C. in 1 minute. As a result, the carbon nanotubes start to grow linearly from the respective catalytic particles without any fusion of each of the catalytic particles. 
     Subsequently, the temperature and an atmosphere are maintained for about 30 minutes. Once the carbon nanotubes start to grow, surfaces of the catalytic particles are covered by carbon, so that any fusion of each of the catalytic particles can be avoided even during the maintenance for about 30 minutes.

TECHNICAL FIELD

The present invention relates to a method of growing a carbon nanotubeand a carbon nanotube growing system.

BACKGROUND

Conventionally, in order to grow carbon nanotubes, a catalytic metalthin film is formed by a sputtering method or a vapor deposition method,and thereafter, the catalytic metal thin film is heated whileintroducing a reduction gas or an inert gas into a chamber, to therebymake the catalytic metal thin film be fine particles (For example, seeJapanese Patent Application Laid-open Nos. 2004-267926 and 2002-530805).After that, a raw gas such as acetylene gas starts to be supplied into achamber, and with the use of a thermal CVD method, a plasma CVD method,a hot filament CVD method or the like, the carbon nanotubes are grown.

However, such conventional methods include a problem that diameters ofthe growing nanotubes are not stabilized, so that characteristics of thecarbon nanotubes tend to vary.

In terms of controlling the diameters of the carbon nanotubes, a methodto grow carbon nanotubes using catalytic particles is described inPatent Document 3. However, even when applying the method described inJapanese Patent Application Laid-open No. 2005-22886, although theexpected object is achieved, the variation of the diameters and thecharacteristics of the carbon nanotubes may arise.

SUMMARY

A manufacturing method of carbon nanotubes according to an aspect of thepresent invention comprises: adhering catalytic particles to an uppersurface of a substrate; and raising a substrate temperature at a speedof 500° C./minute or faster in a chamber with a raw gas containingcarbon atoms previously introduced therein.

A carbon nanotube growing system according to an another aspect of thepresent invention is provided with a catalyst adhering portion adheringcatalytic particles to an upper surface of a substrate, and a thermaltreatment portion raising a substrate temperature at a speed of 500°C./minute or faster in a chamber with a raw gas containing carbon atomspreviously introduced therein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a sectional view showing a method of growing carbon nanotubesaccording to a first embodiment;

FIG. 1B is a sectional view showing the method of growing carbonnanotubes following FIG. 1A;

FIG. 1C is a sectional view showing the method of growing carbonnanotubes following FIG. 1B;

FIG. 1D is a sectional view showing the method of growing carbonnanotubes following FIG. 1C;

FIG. 1E is a sectional view showing the method of growing carbonnanotubes following FIG. 1D;

FIG. 1F is a sectional view showing the method of growing carbonnanotubes following FIG. 1E;

FIG. 2 is a view showing a temperature control in the first embodiment;

FIG. 3 is a view showing details of carbon nanotubes 17;

FIG. 4 is a view showing an example of a temperature control;

FIG. 5A is a SEM micrograph showing carbon nanotubes grown based on anexample No. 1;

FIG. 5B is a view schematically showing the carbon nanotubes grown basedon the example No. 1;

FIG. 6A is an SEM micrograph showing carbon nanotubes grown based on anexample No. 2;

FIG. 6B is a view schematically showing the carbon nanotubes grown basedon the example No. 2;

FIG. 7A is an SEM micrograph showing carbon nanotubes grown based on anexample No. 3;

FIG. 7B is a view schematically showing the carbon nanotubes grown basedon the example No. 3;

FIG. 8 is a view showing a temperature control in the example No. 3;

FIG. 9A is a sectional view showing a method of growing carbon nanotubesaccording to a second embodiment;

FIG. 9B is a sectional view showing the method of growing carbonnanotubes following FIG. 9A;

FIG. 9C is a sectional view showing the method of growing carbonnanotubes following FIG. 9B;

FIG. 9D is a sectional view showing the method of growing carbonnanotubes following FIG. 9C;

FIG. 10A is a view showing another example of a temperature control;

FIG. 10B is a view showing further another example of a temperaturecontrol; and

FIG. 11 is a view showing an example of a temperature control and anatmosphere control.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached drawings.

First Embodiment

First, a first embodiment will be explained. FIGS. 1A to 1F aresectional views showing a method of growing carbon nanotubes accordingto the first embodiment in order of step.

In the present embodiment, first, a silicon oxide (SiO₂) film 12 isformed on a silicon (Si) substrate 11, as shown in FIG. 1A. A thicknessof the silicon oxide (SiO₂) film 12 is, for example, about 350 nm. Next,a resist pattern 13 having a circular opening portion 13 a is formed onthe silicon oxide (SiO₂) film 12. The opening portion 13 a has adiameter of, for example, about 2 μm.

Subsequently, the silicon oxide (SiO₂) film 12 is patterned using theresist pattern 13. As a result, a cylindrical opening portion 14 isformed in the silicon oxide (SiO₂) film 12, as shown in FIG. 1B.

Thereafter, a catalytic layer 15 is formed at a bottom portion of theopening portion 14, as shown in FIG. 1C. As the catalytic layer 15, atitanium (Ti) film having about 1 nm in thickness, for example, isformed.

Next, a plurality of catalytic particles 16 having substantially uniformdiameters are adhered on the catalytic layer 15, as shown in FIG. 1D.The catalytic particle 16 has a diameter of, for example, 5 nm orsmaller. As the catalytic particles 16, cobalt (Co) particles, nickel(Ni) particles, or iron (Fe) particles are used, for example. It shouldbe noted that alloy particles of these elements may also be used. Thecatalytic particles 16 may adhere on the resist pattern 13, as shown inFIG. 1D. A method for adhering the catalytic particles 16 is not limitedin particular. For example, a method described in Japanese PatentApplication Laid-open No. 2005-22886 may be applied.

Next, the resist pattern 13 is removed by ashing or the like, as shownin FIG. 1E. As a result, even when being adhered on the resist pattern13, the catalytic particles 16 are removed.

Subsequently, carbon nanotubes 17 are grown from the catalytic particles16 on the catalytic layer 15, as shown in FIG. 1F. When growing thecarbon nanotubes 17, the silicon (Si) substrate 11 on which thecatalytic layer 15 is formed is delivered into a thermal CVD chamber(not shown) whose internal temperature is, for example, a roomtemperature (R.T.), and a mixed gas of an inert gas and a raw gas isintroduced into the inside thereof. For the mixed gas, a mixed gas ofargon and acetylene in which a mixing ratio thereof is 90:10, forexample, is used. In other words, a mixed gas in which a raw gas(acetylene gas) is diluted by an inert gas (argon gas) is used. Then,after the pressure inside of the chamber is stabilized at 1 kPa, forexample, the temperature inside of the chamber is raised to 510° C. in 1minute, as shown in FIG. 2. As a result, the carbon nanotubes 17 startto grow linearly from the respective catalytic particles 16 without anyfusion of each of the catalytic particles 16.

Next, the temperature and an atmosphere are maintained for about 30minutes, for example. Once the carbon nanotubes 17 start to grow,surfaces of the catalytic particles 16 are covered by carbon, so thatany fusion of each of the catalytic particles 16 can be avoided evenduring the maintenance for about 30 minutes. Subsequently, when themaintenance is completed, the temperature is lowered to the roomtemperature, while keeping the atmosphere.

According to the present embodiment as described above, since thecatalytic particles 16 are adhered on the catalytic layer 15 and the rawgas is already supplied into the chamber before the heating is started,the carbon nanotubes 17 initiate the growth immediately from the startof the heating. Therefore, the catalytic particles 16 do not fusetogether, as described above. Further, since the temperature is raisedat high speed, the fusion of each of the catalytic particles 16 can beprevented further securely. As a result, the diameter of the carbonnanotube 17 is determined depending on the diameter of the adheredcatalytic particle 16. Further, the present embodiment applies thecatalytic particles 16 having the substantially uniform diameters (about5 nm, for example), so that a variation of the diameters of the carbonnanotubes 17 grown from the catalytic particles 16 also becomesextremely small.

Note that, technically speaking, the carbon nanotube 17 which is grownaccording to the above-described embodiment includes a straight portion17 a and a crimped portion 17 b, as shown in FIG. 3. This is because thecarbon nanotube 17 grows linearly when raising a temperature at highspeed, but it grows while being crimped when maintaining thetemperature. When comparing the characteristics of these portions, thestraight portion 17 a has smaller defects and lower resistance values.Therefore, it is preferable to select a condition under which thestraight portion 17 a grows longer. According to the results ofexperiments performed so far by the present inventor, it is favorable toset the pressure inside of the chamber at 0.1 kPa to 30 kPa, and thespeed of raising the temperature at 500° C./minute or faster, forexample. To conduct spike annealing when raising the temperature iseffective. Because when the spike annealing is applied, it is possibleto raise the temperature even at a speed of 500° C./second or faster.Further, the period of time taken for raising the temperature is alsonot limited in particular, and it is set at, for example, more than 30seconds or more than 1 minute.

Further, maintaining the temperature after raising the temperature isunnecessary, so that it is permissible to start to lower the temperatureimmediately after the completion of raising the temperature, as shown inFIG. 4.

Further, the temperature to be achieved by the high-speed temperaturerise may be the one at which the carbon nanotubes can grow, and is setat, for example, 400° C. or higher. The temperature to be maintainedthereafter may also be the one at which the carbon nanotubes can grow.However, when portions being vulnerable to heat such as a low dielectricconstant film exist on the same substrate, the temperature is preferableto be set at 450° C. or lower.

Further, the raw gas is not limited to the acetylene gas, and varioushydrocarbon gases can also be applied.

Further, the catalytic particles may contain titanium (Ti), molybdenum(Mo), palladium (Pd), tantalum (Ta), aluminum (Al), tungsten (W), copper(Cu), vanadium (V), hafnium (Hf) and/or zirconium (Zr), in addition toiron (Fe), cobalt (Co) and/or nickel (Ni). When these elements arecontained in the catalytic particles, there is a case that the carbonnanotubes start to grow at a lower temperature.

Further, when growing the carbon nanotubes, it is permissible torepeatedly perform the treatments of raising the temperature at highspeed and lowering the temperature, as shown in FIG. 10A. In this case,the temperature may be maintained between the periods of raising thetemperature at high speed and lowering the temperature, as shown in FIG.10B. By repeatedly conducting such treatments, it is possible to obtaina carbon nanotube having a characteristic varied in a length directionthereof.

Further, it is also permissible to change the kind of the raw gas, thepressure, the temperature, a temperature gradient and the like in eachtemperature profile. When applying these conditions, the carbonnanotubes can also be grown by performing a control as shown in FIG. 11.

More specifically, first, a temperature is raised at high speed to 510°C. in 1 minute in a mixed gas (1 kPa) of acetylene (C₂H₂) and argon(Ar). As a result, the carbon nanotubes are grown from almost all of thecatalytic fine particles, but, there exists some from which the carbonnanotubes are not grown. This is because the catalytic fine particlesare covered by carbon before the carbon nanotubes start to growtherefrom. Accordingly, the raw gas is once evacuated and oxygen isnewly introduced into the chamber until the pressure in the chamberreaches 1 kPa. Thereafter, the temperature is raised at high speed fromthe room temperature to 510° C. in 1 minute in the oxygen atmosphere. Byconducting this process, the carbon covering the catalytic fineparticles is removed.

Subsequently, the temperature is lowered to the room temperature, andagain, the temperature is raised at high speed to 510° C. in 1 minute inthe mixed gas (1 kPa) of acetylene and argon. As a result, the carbonnanotubes are grown from almost all of the catalytic fine particles fromwhich the carbon nanotubes are not grown at the first time of thehigh-speed temperature rise.

By repeatedly conducting such processes, it is possible to effectivelyutilize the catalytic fine particles. In other words, the carbonnanotubes can be grown from almost all of the catalytic fine particles.As a result, it becomes possible to obtain the carbon nanotubes grown inhigh density that may not be obtained at one time of the high-speedtemperature rise. Note that, a condition(s) under which the temperatureis raised at high speed and/or the oxidation is performed for the secondtime or thereafter may vary from that (those) of the first time.

Note that, to construct a carbon nanotube growing system, a unitadhering catalysts (catalyst adhering portion) and a thermal treatmentunit performing the high-speed temperature rise (thermal treatmentportion) and the like may be provided separately or in combination.

Next, SEM micrographs of the carbon nanotubes actually taken by thepresent inventor are shown in FIG. 5A, FIG. 6A and FIG. 7A. Further,contents of the SEM micrographs shown in FIG. 5A, FIG. 6A and FIG. 7A,respectively, are schematically shown in FIG. 5B, FIG. 6B and FIG. 7B.The carbon nanotubes shown in FIG. 5A and FIG. 5B were grown based on amethod according to the above-described embodiment (example No. 1). Thecarbon nanotubes shown in FIG. 6A and FIG. 6B were grown based on amethod according to the above-described embodiment in which a pressurein the chamber was changed (example No. 2). In the example No. 2, thepressure in the chamber was set at 10 kPa. The carbon nanotubes shown inFIG. 7A and FIG. 7B were grown based on a method according to theabove-described embodiment in which a temperature control was changed(example No. 3). In the embodiment No. 3, after the pressure inside ofthe chamber was stabilized at 1 kPa, the temperature in the chamber wasraised to 510° C. in 30 minutes, as shown in FIG. 8.

As is confirmed by comparing the carbon nanotubes shown in FIG. 5A andFIG. 5B with the carbon nanotubes shown in FIG. 6A and FIG. 6B, as thepressure became higher, the carbon nanotubes with longer straightportions were obtained.

Further, as is confirmed by comparing the carbon nanotubes shown in FIG.5A and FIG. 5B with the carbon nanotubes shown in FIG. 7A and FIG. 7B,as the speed of raising the temperature became faster, the carbonnanotubes with longer straight portions were obtained. Note that also inthe carbon nanotubes shown in FIG. 7A and FIG. 7B, an effect in whichthe diameter variation thereof was small was obtained.

Second Embodiment

Next, a second embodiment will be explained. FIGS. 9A to 9D aresectional views showing a method of growing carbon nanotubes accordingto the second embodiment in order of step.

In the present embodiment, first, a silicon oxide (SiO₂) film 22 isformed on a silicon (Si) substrate 21, as shown in FIG. 9A. A thicknessof the silicon oxide (SiO₂) film 22 is, for example, about 350 nm.

Next, a catalytic layer 25 is formed on the silicon oxide (SiO₂) film22, as shown in FIG. 9B. As the catalytic layer 25, a titanium (Ti) filmhaving about 1 nm in thickness, for example, is formed.

Subsequently, a plurality of catalytic particles 26 having substantiallyuniform diameters are adhered on the catalytic layer 25, as shown inFIG. 9C. The catalytic particle 26 has a diameter of, for example, 5 nmor smaller. As the catalytic particles 26, cobalt (Co) particles, nickel(Ni) particles, or iron (Fe) particles are used, for example. Further,alloy particles of these elements may also be used. A method foradhering the catalytic particles 26 is not limited in particular. Forexample, the method described in Japanese Patent Application Laid-openNo. 2005-22886 may be applied, similar to the first embodiment.

Thereafter, carbon nanotubes 27 are grown from the catalytic particles26 on the catalytic layer 25, as shown in FIG. 9D. The carbon nanotubes27 can be grown using a similar method as is used for growing the carbonnanotubes 17 in the first embodiment.

Also in the second embodiment as described above, the same effect as inthe first embodiment can be obtained.

1. A method of growing a carbon nanotube, comprising: adhering catalyticparticles to an upper surface of a substrate; introducing a raw gascontaining carbon atoms in a chamber at below 400° C.; after introducingthe raw gas, starting raising a substrate temperature at a speed of 500°C./minute or faster in the chamber with the raw gas previouslyintroduced therein.
 2. A method of growing a carbon nanotube,comprising: first raising of a substrate temperature in a chamber with araw gas containing carbon atoms previously introduced therein; andsecond raising of the substrate temperature in the chamber with anoxidizing gas previously introduced therein, wherein said first andsecond raising of the substrate temperature are repeatedly conducted,wherein said first raising comprising: introducing the raw gas in thechamber at below 400° C.; after introducing the raw gas, startingraising the substrate temperature, and wherein said second raisingcomprising: introducing the oxidizing gas in the chamber; afterintroducing the oxidizing gas, starting raising the substratetemperature.
 3. The method of growing a carbon nanotube according toclaim 1, wherein raising the substrate temperature is continued untilthe substrate temperature reaches 400° C. or higher.
 4. The method ofgrowing a carbon nanotube according to claim 1, wherein raising thesubstrate temperature is continued for 30 seconds or longer.
 5. Themethod of growing the carbon nanotube according to claim 1, wherein adiameter of the catalytic particle is 5 nm or smaller.
 6. The method ofgrowing a carbon nanotube according to claim 1, wherein the catalyticparticle contains at least one kind selected from the group consistingof iron (Fe), cobalt (Co) and nickel (Ni).
 7. The method of growing acarbon nanotube according to claim 6, wherein the catalytic particlefurther contains at least one kind selected from the group consisting oftitanium (Ti), molybdenum (Mo), palladium (Pd), tantalum (Ta), aluminum(Al), tungsten (W), copper (Cu), vanadium (V), hafnium (Hf) andzirconium (Zr).
 8. The method of growing a carbon nanotube according toclaim 1, wherein a hydrocarbon gas is used as the raw gas.
 9. The methodof growing a carbon nanotube according to claim 1, wherein the raw gasis diluted by an inert gas.
 10. The method of growing a carbon nanotubeaccording to claim 1, wherein a pressure in the chamber during said stepof raising the substrate temperature is set at 0.1 kPa to 30 kPa. 11.The method of growing a carbon nanotube according to claim 1, furthercomprising maintaining the substrate temperature at which the carbonnanotube can grow, after said raising the substrate temperature.
 12. Themethod of growing a carbon nanotube according to claim 11, wherein atemperature is maintained at 450° C. or lower in said maintaining thesubstrate temperature.
 13. The method of growing a carbon nanotubeaccording to claim 1, wherein the raw gas is introduced at a substantialroom temperature.